This invention pertains to non-contacting distance-measuring apparatus, and more particularly, to such apparatus which employs alternately energized light sources, and a photodetector, to perform such measuring. For the purpose of illustration herein, a perferred embodiment of the invention is described in connection with monitoring the surface profiles of log cants which are being prepared for feeding into an edger in a saw mill.
There are numerous applications, particularly in the processing of different materials, where it is economically important, and even critical, to monitor closely the surface profile of an object during its processing. For example, in the wood products industry, prudent handling of logs in a saw mill dictates the necessity for close monitoring of the sawn products in order to maximize lumber yield, and hence economy. One of the areas in a saw mill where strong improvement has been required has been in the edging of log cants to remove what are referred to as the wane areas in a cant. As is well known to those skilled in the art, a cant is that which is sawn directly from a whole log, and the wane in a cant appears at the edges thereof which are defined by the outside circumference of the original log. In the past, a variety of techniques, including manual "eye balling", have been used to determine where, in relation to the saw line for an edger saw, a particular cant should be placed to remove its wane areas, to yield the largest possible board of the highest quality.
A general object of the present invention is to provide apparatus, usable in a setting like that just described, to perform, as accurately and simply as possible, such a surface-distance measuring and monitoring operation.
More particularly, an object of the invention is to provide such apparatus which, within a definable and selectively variable range, is capable, with a high degree of resolution, of locating the surface of an object relative to opposite sides of a defined datum plane.
According to a preferred embodiment of the invention, described herein, the same features two pairs of light sources which are disposed on one side of such a defined plane, and on opposite sides of what is referred to as a reflection viewing plane which is normal to the datum plane. In each of the pairs of sources, two light-emitting diodes are used which are energized alternately to create, on opposite sides of the datum plane, and with regard to the reflection viewing plane, alternate upper and lower zones of illumination which may be thought of as intersecting generally along a common line which is defined by the line of intersection of the datum and viewing planes.
A photodetector, which is on the same side of the datum plane as the light sources, looks for reflections along the viewing plane, and produces an output signal whose level directly follows the level of light reflection from the sources returning from an object's surface which is illuminated by the sources. The output signal from the photodetector is gated into a sample-and-hold circuit in such a manner that its signal is directly interpretable not only to indicate the distance of a reflecting surface from the datum plane, but also the side of such plane on which the reflecting surface is located. In other words, the output signal from the photodetector is gated to coincide with the alternate energizing times for the light sources, whereby its output signal can be determined as having resulted from reflected illumination resulting from illumination by particular ones of the sources. With two different sources in each pair producing preferential illumination zones on opposite sides of the datum plane, and with the output signal from the photodetector gated to sample-and-hold circuits, the side of the datum plane on which the reflecting surface resides is easily determinable.
Employed in the apparatus of the invention, in the circuitry which monitors the output signal from the photodetector, is a differential amplifier in which what might be thought of as the "viewing" range of the apparatus is definable and selectively variable to expand and contract the range. For example, the range not only may be expanded and contracted, but also may be shifted as a whole relative to what has been referred to hereinabove as the datum plane. In other words the range may have a major portion shifted either above or below the datum plane, depending upon the particular application.
The apparatus of the invention is easily installed in a variety of settings without requiring any significant modification of existing equipment, operates at extremely low power levels, and requires virtually no maintenance.
These and other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.